The present invention relates to the field of off-line switching power supplies.
An off-line switching power supply receives power from an alternating-current (AC) power source and provides a voltage-regulated, direct-current (DC) output that can be used to power a load. An exemplary off-line power supply includes a power factor correction (PFC) stage and a DC-to-DC converter stage. The PFC stage receives the AC input signal, performs rectification and maintains current drawn from the AC source substantially in phase with the AC voltage so that the power supply appears as a resistive load to the AC source. The DC-to-DC converter stage receives the rectified output of the PFC stage and generates the voltage-regulated, DC output which can be used to power the load. The rectified output of the PFC stage is typically at higher voltage and is more loosely regulated than the output of the DC-to-DC stage.
An off-line power supply typically includes control circuitry, including analog and digital circuitry, that operates at relatively low voltage levels of approximately 5 to 15 volts DC. However, voltage levels within the power supply can reach levels of several hundred volts. For example, the rectified output of the PFC stage can be regulated to approximately 380 volts DC or higher.
Additionally, it is increasingly important for power supplies to operate efficiently so as to minimize power usage.
Therefore, what is needed are improved techniques for accommodating different voltage levels within a switching power supply while achieving efficient operation.